题解 | #统计作答次数#
统计作答次数
https://www.nowcoder.com/practice/45a87639110841b6950ef6a12d20175f
select count(*) total_pv, sum( case when submit_time is not null then 1 else 0 end ), count(distinct case when submit_time is not null then exam_id else null end) from exam_record